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Reactions on a drawbridge

  1. Apr 6, 2007 #1

    danago

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    Hi. Not directly a specific homework question, but it will help with some of my questions.

    When the bridge is flat, why is the reaction force from the wall on the bridge angled upwards? Why is it not horizontal, along the length of the bridge?

    Sorry if i was a little vague.

    Thanks,
    Dan.
     
  2. jcsd
  3. Apr 6, 2007 #2

    Dick

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    If the force were only horizontal, how would that keep it from falling? I'm also sorry to be vague.
     
  4. Apr 7, 2007 #3

    danago

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    Hmm ok. If it was a frictionless wall, would it be possible for an angled reaction force to exist?
     
  5. Apr 7, 2007 #4

    Doc Al

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    I don't understand the situation. Are you saying that the drawbridge is held up by friction? How is the bridge attached to the wall? What pulls the bridge up and down?
     
  6. Apr 7, 2007 #5

    Dick

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    Nearest I can come to having it make sense is that the bridge is being compressed against the wall. So there two forces. There is the horizontal wall reaction force to the normal force of compression. And there would be a vertical static frictional force holding the thing up. So the combination of these two forces can be 'angled upwards'. If it's a frictionless wall, the bridge will fall.
     
    Last edited: Apr 7, 2007
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